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Date:   Fri, 21 Aug 2020 09:43:43 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, davem@...emloft.net, brouer@...hat.com,
        echaudro@...hat.com, sameehj@...zon.com, kuba@...nel.org
Subject: Re: [PATCH net-next 3/6] net: mvneta: update mb bit before passing
 the xdp buffer to eBPF layer

On Aug 20, Maciej Fijalkowski wrote:
> On Wed, Aug 19, 2020 at 03:13:48PM +0200, Lorenzo Bianconi wrote:
> > Update multi-buffer bit (mb) in xdp_buff to notify XDP/eBPF layer and
> > XDP remote drivers if this is a "non-linear" XDP buffer
> > 
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> >  drivers/net/ethernet/marvell/mvneta.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> > index 832bbb8b05c8..36a3defa63fa 100644
> > --- a/drivers/net/ethernet/marvell/mvneta.c
> > +++ b/drivers/net/ethernet/marvell/mvneta.c
> > @@ -2170,11 +2170,14 @@ mvneta_run_xdp(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
> >  	       struct bpf_prog *prog, struct xdp_buff *xdp,
> >  	       u32 frame_sz, struct mvneta_stats *stats)
> >  {
> > +	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> >  	unsigned int len, data_len, sync;
> >  	u32 ret, act;
> >  
> >  	len = xdp->data_end - xdp->data_hard_start - pp->rx_offset_correction;
> >  	data_len = xdp->data_end - xdp->data;
> > +
> > +	xdp->mb = !!sinfo->nr_frags;
> 
> But this set is not utilizing it from BPF side in any way. Personally I
> would like to see this as a part of work where BPF program would actually
> be taught how to rely on xdp->mb. Especially after John's comment in other
> patch.
> 

Sameeh is working on them. I did not include the patches since IMO they are
not strictly related to this series. I will include Sameeh's patches in v2.

Regards,
Lorenzo

> >  	act = bpf_prog_run_xdp(prog, xdp);
> >  
> >  	/* Due xdp_adjust_tail: DMA sync for_device cover max len CPU touch */
> > -- 
> > 2.26.2
> > 
> 

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